Here's a position-by-position look at who is moving up the rankings, who is moving down and who owners should keep an eye on in May. Full hitter and pitcher rankings are available to Fantasy Source members.

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UP: Masahiro Tanaka, Yankees (#11). Tanaka has been better than advertised in his first month of big league action, posting a 2.27 ERA and 0.93 WHIP to go with a surprisingly high 11.6 K/9 through five starts. There's bound to be some regression as hitters get a look at Tanaka, but he's clearly the real deal.

DOWN: Shelby Miller, Cardinals (#48). This isn't just a slow start for Miller; his struggles trace back to late last season. In fact, his drop-off seems to trace back to Aug. 7 when he left a start against the Dodgers early after being hit in the elbow by a comebacker. In 21 starts before that game, Miller had a 9.8 K/9 and 2.6 BB/9; in 15 starts since, he has a 6.6 K/9 and 4.5 BB/9. Coincidence? Probably, but at least it's a possible reason for the decline.

KEEP AN EYE ON: Nathan Eovaldi, Marlins (#37). The hard-throwing righthander is off to a hot start and he's getting a gift from the scheduling gods with his projected May opponents: at home against the Mets, at San Diego, at San Francisco, at home against the Phillies, at Washington and maybe at home against the Braves. His stock should keep rising.